A variety of approaches to imaging using optical coherence tomography (OCT) are known. Such systems may be characterized as Fourier domain OCT (FD-OCT) and time domain OCT (TD-OCT). FD-OCT generally includes swept source (SS) and spectral domain (SD), where SD systems generally use spectrometers rather than a swept source. TD systems generally rely on movement of a mirror or reference source over time to control imaging depth. In contrast, for FD-OCT, the imaging depth may be determined from a Fourier transform of the acquired spectrum, rather than by the range of a physically scanned mirror. Specifically, in FD-OCT, the number of samples of the spectrum may be used to control the imaging depth, with a greater number of samples of spectrum providing a deeper imaging capability.
OCT imaging systems are well known for use in ophthalmic imaging, and have been applied commercially for posterior imaging of the retina (hereinafter “posterior imaging systems”), and for anterior imaging of the cornea and the anterior chamber (hereinafter “anterior imaging systems”). Posterior imaging systems for imaging the posterior region of the eye and anterior imaging systems for imaging anterior segments of the eye may require different penetration depths, imaging depths, focal positions, and/or scanning optics. Generally, posterior imaging systems developed for high quality posterior imaging applications have not been applicable to high quality anterior applications. Conversely, anterior imaging systems developed for high quality anterior imaging applications have not been applicable to high quality posterior applications
In particular, posterior imaging systems developed for posterior imaging typically utilize the cornea and the lens of the eye as effective components of the integrated imaging system. The imaging system including these anterior components of the eye is designed to focus the scanning beam on the retina, approximately 24 mm from the cornea surface. Additionally, the scanned beam is designed to angularly pivot around a point centered in the neighborhood of the iris and the lens, appropriate for scanning the curved retina at the rear of the posterior segment.
A sample arm of a conventional posterior imaging system will now be discussed with respect to FIG. 1. As illustrated therein, the posterior imaging system 100 includes a collimation optic 105, a scanning optic 110, a scan lens 121, an objective lens set 150/160 and a human eye (sample) 125. As illustrated, the human eye 125 includes an anterior segment 130, a posterior segment 135 and posterior pole 145. The collimation optic 105 is configured to collimate the light diverging from a fiber optic output. The scanning optic 110 may be, for example, a mirror mounted on a galvonometer, and may be configured to scan a beam over the scan lens 121. The scan lens 121 may be configured to parallelize the light coming off the scanning optic 110. In particular, the ray bundles 109 coming off the scanning optic 110 are diverging, but the rays 107 within the ray bundles 109 are collimated. After passing through the scan lens 121, the ray bundles 109 are made parallel, and the rays within each bundle are focused to a point between the scan lens and objective lens, thus they are diverging again when reaching the objective lens set. The objective lens set 150/160 is configured to collimate the rays 107 within the ray bundles 109, which are made to converge through the iris of the human eye 125 as a pivot point. The cornea and lens of the human eye serve to focus the rays within each bundle onto a separate point on the retina, thus imaging the intermediate focus between the scan lens and objective lens set onto the retina. In other words, posterior imaging systems 100 are designed to use the sample (human eye 125) as a component of the system 100.
Posterior imaging systems are discussed in detail in, for example, In Vivo Retinal Imaging by Optical Coherence Tomography by Swanson (Optics Letters, Vol. 18, No. 21 (Nov. 1, 1993)) and U.S. Pat. No. 5,321,501 to Swanson, the disclosures of which are hereby incorporated herein by reference as if set forth in their entirety.
Anterior imaging systems developed for anterior imaging generally treat the cornea as an object of the imaging system, rather than a component, and are generally designed to image the depth, width and structure of the anterior chamber from corneal surface to iris and lens. Such systems place the focus approximately 20 mm forward of the posterior imaging system, have an imaging depth of 6.0 to 10.0 mm, in contrast to the 0.5 to 2.0 mm typically required in posterior imaging systems, and are supported by telecentric or near-telecentric scanning geometries rather than the pivoting geometry used in the posterior imaging systems, for example, the posterior imaging system of FIG. 1.
A sample arm of a conventional anterior imaging system 200 will now be discussed with respect to FIG. 2. As illustrated therein, the anterior imaging system 200 includes a collimation optic 205, a scanning optic 210, a scan/objective lens 220 and a human eye as a sample 225. As illustrated, the human eye 225 includes an anterior segment 230, a posterior segment 235 and posterior pole 245. The collimation optic 205 is configured to collimate the light diverging from a fiber optic output. The scanning optic 210 may be, for example, a mirror mounted on a galvonometer, and may be configured to scan a beam over the scan/objective lens 220. The scan/objective lens 220 may be configured to parallelize and focus the light coming off the scanning optic 210. In particular, the ray bundles 209 coming off the scanning optic are diverging, but the rays 207 within the ray bundles 209 are collimated. After passing through the scan/objective lens 220, the ray bundles 209 are parallel, but the rays 207 within the ray bundles 209 are focusing on the object being imaged, here the anterior segment 230 of the human eye 225.
Anterior imaging systems are discussed in detail in, for example, Micrometer-Scale Resolution Imaging of the Anterior Eye In Vivo with Optical Coherence Tomography by Izatt et al. (Ophthalmology, Vol. 112, pp. 1584-1589 (December 1994)) and Real-time Optical Coherence Tomography of the Anterior Segment at 1310 nm by Radhakrishnan et al. (Ophthalmology, Vol. 119, pp. 1179-1185 (August 2001)), the disclosures of which are hereby incorporated herein by reference as if set forth in their entirety.